X-ray absorption and infrared reflectance of poled silica glass for second harmonic generation

Structural alterations induced by a thermal poling treatment which is at the origin of second harmonic generation in a Herasil silica glass are studied by x-ray absorption near-edge spectroscopy (XANES). Multiple scattering calculations are performed to explain the experimental O–K edge XANES shape of unpoled surfaces of the glass and then to interpret modifications resulting from poling. The observations are consistent with emergence of disorder by breaking Si–O bridging bonds which are not completely removed by a thermal depoling treatment. Fourier transform infrared spectroscopy shows modifications of nonbridging oxygen bonds which are coherent with a model involving a protons migration during poling. Moreover, a partial anisotropy in the direction of the electrostatic field which is applied during the poling treatment is observed.